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manual: document builtins.functionArgs

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The text is just a conversion of comment from src/libexpr/primops.cc
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Vladimír Čunát 2015-12-30 08:42:41 +01:00 • committed by Eelco Dolstra
parent 5eb93556f1
commit 29c0199d5c
2 changed files with 20 additions and 2 deletions
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20
doc/manual/expressions/builtins.xml
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@ -335,7 +335,7 @@ stdenv.mkDerivation {
</varlistentry>
<varlistentry><term><function>builtins.foldl’</function>
<varlistentry><term><function>builtins.foldl’</function>
<replaceable>op</replaceable> <replaceable>nul</replaceable> <replaceable>list</replaceable></term>
<listitem><para>Reduce a list by applying a binary operator, from
@ -348,6 +348,24 @@ stdenv.mkDerivation {
</varlistentry>
<varlistentry><term><function>builtins.functionArgs</function>
<replaceable>f</replaceable></term>
<listitem><para>
Return a set containing the names of the formal arguments expected
by the function <replaceable>f</replaceable>.
The value of each attribute is a Boolean denoting whether the corresponding
argument has a default value. For instance,
<literal>functionArgs ({ x, y ? 123}: ...) = { x = false; y = true; }</literal>.
</para>
<para>"Formal argument" here refers to the attributes pattern-matched by
the function. Plain lambdas are not included, e.g.
<literal>functionArgs (x: ...) = { }</literal>.
</para></listitem>
</varlistentry>
<varlistentry><term><function>builtins.fromJSON</function> <replaceable>e</replaceable></term>
<listitem><para>Convert a JSON string to a Nix